The subject invention relates to magnetic disk recording systems and particularly to "spiral" track recording therewith.
Those in the magnetic recording arts recognize the need for improved techniques and associated apparatus for better, more effective data detection. Efforts have continued for sometime now to fill this need.
One conventional type of recording system involves "concentric track" recording where a magnetic disk [typically used as peripheral memory equipment in a computer system to provide temporary or permanent information storage during computer operations] is recorded-upon in concentric tracks. In one well-known configuration, one, or several, such disks are mounted to be rapidly rotated in operative relation with transducer means, the disk having a multi-track magnetic recording surface on at least one of its faces. One, or several, recording heads are, in turn, adapted to be positioned along each disk-face--i.e., to register with any selected one of the concentric recording tracks on the disk to record and detect data signals along any track.
Workers will recognize that optimal use of such media requires that information be recorded with minimal effort and at the highest possible density. However, concentric-track disks--unlike tape--present the problem of "limited-length record fields".pi.(or "closed-ended fields") whereby the defined (circumferential) length of a given track usually compels one (e.g., a Programmer, a User, the Designer) to either waste "terminal space" or interrupt a data field which happens to occur there. For instance, if a given track fills up with data fields until only a fifty-bit segment remains and the next convenient record subset to be recorded is 60 bits long, one must either shift to another recording track (wasting this 50-bit space), or interrupt this 60-bit subset; paying the usual price in "overhead" (e.g., added bits to note the interruption, identify the continuation, etc.; and the added complexity in software labor, etc.).
But, with tape, or any like record offering "open-ended fields", this problem will not arise (except in rare instances; e.g., at "end-of-tape"). This invention is directed to providing spiral track disk recording which offers such "open-ended fields" and other advantages.
Workers will recognize that, for the typical magnetic disk system, a recording head is translated radially across the disk so that the magnetic transducer gaps mounted therein may be selectively positioned adjacent a selected recording track. In this way only a few transducer gaps need be used for recording and reading data on a number of disk tracks--but to practically implement such a system, one must maintain very precise control of head location relative to the tracks--and this typically must be done very quickly to minimize access time for the computer system served.
For instance, with disks used in a random access magnetic memory the data bits are recorded in concentric circular tracks so there is a continual need to secure and maintain very accurate registry of a magnetic transducer with a selected track. Unfortunately, the precision of the transducer-positioning system will determine track spacing tolerances and accordingly will influence data storage efficiency (bit compression) significantly--that is, the number of characters per unit memory area will depend upon the accuracy of transducer positioning. Workers have attempted in various ways to improve the accuracy of transducer positioning, for "servoing" the transducer onto disk tracks. Such systems have commonly employed "position signal" tracks (or track sectors) interspersed with the data tracks and have also required a special servo transducer detector to detect the "position-signals". Other approaches use "track-on-data" techniques (e.g., see Parent U.S. Ser. No. 807,155 cited above). This invention can allow one to avoid all inter-track re-positioning difficulties by adopting "spiral" recording--whereby, once a track is located, one merely "follows" the track for n revolutions, keeping centered thereon.
Workers in these arts will recognize that it is quite desirable to "track-on-data", that is to somehow use an area devoted to "data-bits" (i.e., "information signals" developed from certain magnetic transitions) to also provide position control signals which may be fed to a positioning servo and control the positioning and/or alignment of a transducer relative to a recorded track. Obviously, such a technique can eliminate the need for a separate "servo" recording unit and related separate recording zones for servo data (such as separate servo disks or separate servo tracks, or track-sectors, typically seen in conventional magnetic recording systems), since the data-transducer and the data-recording zones may be used for servo-bits too. The invention accomplishes this, providing a "spiral" mode of recording with "track-on-data" capability (e.g., as opposed to other methods of centering--see parent Ser. No. 807,155 for citations to some such), with no need for separate servo tracks and providing a "servo transducer" which is integrated with a "data transducer", with servo-bits being incorporated into the data recording zones as desired.